1. Field of the Invention
The present invention relates to a method for inhibiting trimethylamine formation, and more particularly to a method for inhibiting trimethylamine formation comprising a step of incorporating trehalose and/or maltitol into a product to be treated, an edible fishery product which trimethylamine formation is inhibited by the method, a trimethylamine formation inhibitory agent comprising trehalose and/or maltitol as effective ingredients, and uses thereof.
2. Description of the Prior Art
It is known that sound or fresh fishery products scarcely smell but they develop a bad smell due to the formation of trimethylamine, a volatile compound as a main causative of a characteristic unpleasant fish smell, formed easily when losing freshness or treated with processings of drying, grilling, boiling, etc. As a method to reduce such unpleasant smell, there has long been used a method for cooking fishery products using spices such as capsicum, pepper, wasabi (Japanese horseradish), Japanese pepper, garlic, and ginger. Such method, however, is not one of lowering the formation of trimethylamine per se as a main causative of fish smell, but one for masking unpleasant smell only by adding a strongly-stimulative taste or flavor. Thus, the know method has a drawback that it may even change a satisfactory flavor, taste, or color inherent to fishery products.
For the last few years, there has been used a method for masking smell using the enclosing action by cyclodextrins. This method, however, has the following drawbacks: Once-enclosed substances as causative of fish smell are easily replaced with other substances, that are susceptive to receive the enclosing action, to release unpleasant smell; and the masking effect of unpleasant smell is not satisfactory. Japanese Patent Kokai No. 289,206/95 discloses a method for removing unpleasant raw smell of extracts of fishery products such as stocks produced in their cooking and broths produced in their steaming, which method comprises adding and dissolving saccharides to and in the extracts, and heating the resulting mixtures at a relatively-high temperature of 125xc2x0 C. or 130xc2x0 C. to remove the unpleasant raw smell of the extracts. In this publication it is shown that such method has a drawback in that it easily imparts a scorched smell to the extracts because the method needs an excessively-high temperature treatment. Thus, the prior art techniques are limited as to how to mask or remove the once-formed unpleasant fish smell and have an insufficient effect with many accompanying drawbacks.
In view of the conventional drawbacks of prior arts, the present invention was made based on a completely novel technical conception, and the objects according to the present invention are to provide a method for inhibiting the formation of unpleasant fish smell per se, an edible fishery product wherein trimethylamine formation is inhibited by the above method, and a novel trimethylamine formation inhibitory agent, as well as its uses.
To overcome the above objects, the present inventors continued studying on the use of saccharides; they studied the influence of saccharides on their inhibitory effect on trimethylamine formation from trimethylamine oxide in the presence of saccharides and trimethylamine oxide as a precursor of trimethylamine. As a result they found that, as compared with other saccharides, trehalose and/or maltitol unexpectedly exert a strong inhibitory effect on the formation of trimethylamine per se, and they confirmed that the formation is strongly inhibited similarly as above by incorporating trehalose and/or maltitol into edible parts of fishery products. Thus they accomplished this invention. The present invention was made based on a technical conception that it fundamentally inhibits trimethylamine formation through the study of trimethylamine formation per se that is deemed as a main causative of the unpleasant fish smell. The technical concept has never been known, so the present technical object is novel in itself. The present invention, which comprises a step of inhibiting the formation of trimethylamine per se by incorporating trehalose and/or maltitol into products to be treated, is novel because no disclosure and no indication about the present invention is found in the prior art. In other words, all the objects and constructions of the present invention are novel, and the effect is also novel and outstanding.
The first object of the present invention is to provide a method for inhibiting trimethylamine formation, which is characterized in that it comprises a step of incorporating trehalose and/or maltitol into products to be treated; the second object is to provide an edible fishery product which trimethylamine formation is inhibited by preserving and/or processing raw fresh fishery products in the presence of trehalose and/or maltitol; and the third object is to provide a trimethylamine formation inhibitory agent comprising trehalose and/or maltitol as effective ingredients and uses thereof. Any trehalose and/or maltitol can be used in the present invention independently of their origin and property as long as they inhibit the formation of trimethylamine. The trehalose usable in the present invention includes, for example, those in the form of a syrup, hydrous crystal, and anhydrous crystal, which are produced by the methods as disclosed in Japanese Patent Kokai Nos. 170,977/95 and 213,283/95, can be arbitrarily used. In particular, xe2x80x9cTREHAOSE(copyright)xe2x80x9d, a high-purity hydrous crystalline trehalose commercialized by Hayashibara Shoji, Inc., Okayama, Japan, can be advantageously used. The maltitol usable in the present invention includes, for example, those in the form of a syrup and an anhydrous crystal which are produced by the methods as disclosed in Japanese Patent Kokoku Nos. 13,699/72 and 2,439/88, can be arbitrarily used. In particular, xe2x80x9cMABIT(copyright)xe2x80x9d, a crystalline maltitol anhydride commercialized by Hayashibara Shoji, Inc., Okayama, Japan, can be advantageously used. Mixtures obtained by mixing commercially available trehalose and maltitol in a free proportion and those obtained by hydrogenating trehalose and maltose as disclosed in Japanese Patent Kokai No. 73,482/96 can be arbitrarily used as mixtures of trehalose and maltitol. The trehalose and/or maltitol usable in the present invention should not be those with a relatively-high purity, and if necessary they can be used in combination with one or more another saccharides listed below as long as the other saccharides do not hinder the trimethylamine formation inhibitory effect; reducing sugars such as glucose, maltose, maltotriose, and maltotetraose; non-reducing saccharides such as sorbitol, maltotritol, and maltotetraitol; and cyclodextrins and their related compounds such as xcex1-, xcex2- and xcex3-cyclodextrins and derivatives thereof.
To effectively increase the trimethylamine formation inhibitory effect, acids can be arbitrarily used in combination with trehalose and/or maltitol to adjust edible parts of fishery products to neutral or acid pHs, preferably, pHs of around 5 to around 7, and more preferably, pHs of around 6 to around 7. Examples of the acids, conventional organic acids such as acetic acid, lactic acid, citric acid, tartaric acid, malic acid, and gluconic acid can be preferably used, and if necessary inorganic acids can be also used. If need be, one or more of the aforesaid spices; flavor-enhancers of amino acids and nucleic acids; liquors including sakes, sweet sakes, brandies, and alcohols; water-soluble polysaccharides such as pectin, alginic acid, and pullulan; and inorganic salts such as salt, potassium chloride, magnesium chloride, and phosphates can be used to exert a satisfactory masking effect.
The edible fishery products according to the present invention mean edible products consisting of or comprising edible parts of fishery products, and compositions comprising edible parts of fishery products, all of which should exert a satisfactory inhibitory effect on the formation of trimethylamine from edible parts of raw fishery products. Preferably, the trehalose and/or maltitol can be homogeneously incorporated into products to be treated in an amount of at least about 0.1 w/w % (the wording xe2x80x9cw/w %xe2x80x9d is abbreviated as xe2x80x9c%xe2x80x9d, hereinafter) of the trehalose and/or maltitol in total, more preferably at least about 0.2% but less than 30%, and most preferably at least of about 0.5% but less than 20%. Usually, the trehalose and/or maltitol could not exert a sufficient trimethylamine formation-inhibitory effect when used in an amount of less than 0.1%, and they tend to excessively sweeten edible products when used in an amount of at least 30%. However, they can be even used in such an amount of 30% or higher when used in products such as foods of delicate flavor, snack foods, and confectionery-type foods, which are rather preferably be sweetened. The content of trehalose and/or maltitol can be arbitrarily increased as much as possible to process up to the desired products in which trehalose hydrate and/or maltitol anhydride are crystallized, and having a lesser hygroscopicity and a satisfactory stability.
The wording xe2x80x9cincorporatingxe2x80x9d as referred to in the present invention means xe2x80x9ccoexisting by contactingxe2x80x9d, i.e., in the case of incorporating trehalose and/or maltitol into edible parts of fishery products, any means can be used in the present invention as long as it exerts an inhibitory effect on the formation of trimethylamine from edible parts of fishery products independently of the methods used for incorporation. Preferably, it can be favorable to incorporate trehalose and/or maltitol into edible parts of raw fishery products by contacting the saccharide(s) with the edible parts in aqueous media as homogeneously as possible. For example, when the edible parts of raw fishery products are in a juicy form such as in a liquid or paste form, either trehalose and/or maltitol in the form of a powder, crystal, or solid can be incorporated into the edible parts by dissolving to homogeneity as much as possible under mixing conditions, or trehalose and/or maltitol in the form of a syrup can be also incorporated into the edible parts by mixing to homogeneity as much as possible.
When the edible parts of raw fishery products used in the present invention are in a solid form, they are first treated with water to give a watery form such as in a liquid or paste form, then treated similarly as above to incorporate trehalose and/or maltitol; or the edible parts in a solid form are incorporated with trehalose and/or maltitol in a manner such that the saccharides are prepared into a syrup, then the edible parts are dispersed, dissolved, or suspended in the syrup to contact with the saccharides as homogeneously as possible. When the edible parts of fishery products are those of their edible tissues in an intact form or a minced form, they are sprayed and mixed with trehalose and/or maltitol in a powdery or crystalline form to dissolve and incorporate the saccharides, or they are soaked in a syrupy product containing trehalose and/or maltitol to incorporate the saccharide(s) as homogeneously as possible.
The wording xe2x80x9cedible parts of fishery productsxe2x80x9d as referred to in the present invention means proteinaceous edible parts from aquatic animals including, for example, fishes such as bluefin tunas, swordfishes, skipjack tunas, yellowtails, Japanese Spanish mackerels, saithes, flatfishes, olive flounders, barracudas, croakers, blue drums, sea breams, sharks, conger eels, eels, puffers, Japanese shads, sardines, horse mackerels, chub mackerels, flathead grey mullets, Pacific herrings, Japanese capelines, chum salmons, and masu salmons; shellfishes such as Japanese fresh water clams, short-necked clams, Japanese hard clams, oysters, scallops, Japanese cockles, bloody clams, whelks, Thomas""s rapa whelks, horned turbans, and abalones; crustaceans such as shrimps, crabs, and giant clams; molluscans such as octopuses and squids; and echinoderms such as sea urchins and sea cucumbers. The edible parts of these fishery products are, for example, tissues and organs of the fishery products such as meats, visceras, spawns, bloods, bones, and skins; and derivatives thereof obtained, for example, by mincing and grinding.
According to the present invention, raw edible parts of the above fishery products are directly or after minced or ground incorporated with trehalose and/or maltitol, and the resulting products can be in usual manner treated with one or more processings such as drying, soaking, grilling, boiling, steaming, and frying to produce the desired edible fishery products in which the trimethylamine formation is effectively inhibited. It was found that fillets of raw fish meats and spawns of salmon-, herring-, and salted Alaska pollack-roes are contacted with trehalose and/or maltitol for preservation, for example, under freezing or cooling conditions at preferable temperatures of 5xc2x0 C. or lower, whereby naturally-occurring trimethylamine formation is strongly inhibited, resulting in a freshness being kept for a relatively-long period of time. The edible fishery products, in which the trimethylamine formation is inhibited by incorporating trehalose and/or maltitol, include, for example, stockfishes such as opened and dried barracudas and horse mackerels, dried mirin-seasoned Pacific sauries and puffers, squids dried overnight, and dried cuttlefishes; boiled and dried fishes such as fine wrinkles, dried sea slugs for broth, and dried shrimps; vinegar-seasoned Japanese shads, small sea breams, and chub mackerels; products pickled with salt such as Japanese Spanish mackerels and sea breams preserved in miso, shrimps preserved in koji, salted opossum shrimps, salted squids, slightly salted salmons, and sea breams steamed with salt; fish jelly products such as boiled fish pastes, chikuwas (a kind of fish paste), Japanese deep-fat fried foods, fish meat sausages, and fish meat hams; foods of delicate flavors such as cleaved and dried Japanese common squids, mirin-seasoned puffers, and dried products of steamed shellfishes; foods boiled down in soy such as small fishes, shellfishes, and Japanese common squids; and canned and bottled products such as edible parts of fishes, shellfishes, crustaceans, and mollusks, all of which are boiled in water, as well as canned and bottled edible products. According to the present invention, a desired trimethylamine formation inhibitory effect is attained and a variety of appetite-stimulating cooked foods can be obtained by using trehalose and/or maltitol when cooking daily dishes such as boiled foods, roasted foods, steamed foods, and fried foods, as well as foods served in pots such as soups, boiled fishes, boiled vegetables, and Japanese hotchpotches.
The present invention is arbitrarily used to inhibit trimethylamine formation by incorporating the present trimethylamine formation inhibitory agent containing trehalose and/or maltitol as effective ingredients into edible parts of raw fishery products. The content of trehalose and/or maltitol as effective ingredients for the trimethylamine formation inhibitory agent is an amount that exerts a desired inhibitory effect on the formation of trimethylamine form edible parts of raw fishery products; Usually, it is at least about 10%, preferably at least about 20%, and more preferably at least about 50% to the agent, on a dry solid basis (d.s.b.). The trimethylamine formation inhibitory agent according to the present invention can be arbitrarily prepared into those which consist of trehalose and/or maltitol, and if necessary one or more another substances selected from the above mentioned reducing saccharides, non-reducing saccharides, cyclodextrins, spices and condiments, sours, flavor-enhancers, alcohols, water-soluble polysaccharides, and inorganic salts can be arbitrarily used in combination to impart the present agent a flavor-improving effect in addition to the trimethylamine formation inhibitory effect. If necessary, adequate amounts of conventional flavor-imparting agents, color-imparting agents, food preservatives, food stabilizers, etc., can be freely used in combination. The trimethylamine formation inhibitory agent thus obtained should not be restricted to a particular shape or form, and it can be those in the form of a syrup, powder, crystal, granule, and tablet. The agent can be used independently of its use as long as it can be used in edible parts of raw fishery products to exert a desired trimethylamine formation inhibitory effect. For example, such an agent can be used in accordance with the aforesaid method for incorporating trehalose and/or maltitol into edible parts of raw fishery products to inhibit the formation of trimethylamine from the edible parts; After incorporating the trimethylamine formation inhibitory agent into edible parts of raw fishery products, the resulting products are preserved and/or processed, and more concretely, the dose of trehalose and/or maltitol, as effective ingredients, to the edible parts and the preserving and/or processing conditions can be selected similarly as in the above, resulting in an exertion of satisfactory trimethylamine formation inhibitory effect on edible parts of fishery products and resulting in a readily production of edible fishery products with a satisfactory taste and flavor. The combination use of the present trimethylamine formation inhibitory agent and a seasoning(s) such as a soy sauce, miso, vinegar, sweetened sake, synthetic mirin, amino- or nucleic-seasoning, and salt can advantageously exert a desired trimethylamine formation inhibitory effect and provide flavorful daily dishes and foods served in pots.
As described above, the edible fishery products as referred to in the present invention are still be satisfactory edible fishery products having a desired trimethylamine formation inhibitory effect and edible products or compositions containing the same, all of which are flavorful and tasteful edible products, even after they are preserved under cooling or freezing conditions at about 5xc2x0 C. or lower, or processed with treatments such as drying, soaking, grilling, boiling, steaming, and frying.
The following experiments describe the present invention in detail:
Into 20-ml vials were placed two milliliters aliquots of 5% aqueous trimethylamine oxide containing 0-5% of either saccharides consisting of trehalose, maltitol, sucrose and maltose as testing saccharides, and 0.2M phosphate buffer (pH 7.0), and the vials were heated at 100xc2x0 C. for three hours and cooled to ambient temperature. Trimethylamine in each solution was quantified by the Picrate method disclosed in Method for Food Analysis, edited by the editorial board of Food Analysis in Japanese Society for Food Science and Technology, Tsukuba, Japan, pp. 674-676 (1982).
The results are in Table 1.
As evident from the results in Table 1, it was revealed that, as compared with the system with no saccharide, the system coexisted with trehalose or maltitol strongly inhibited the formation of trimethylamine from trimethylamine oxide. No substantial inhibitory effect was found in the system with sucrose or maltose.
A chub mackerel""s meat was minced with a mincer, and 10 g aliquots of the resulting mince were placed in 50-ml vials. To each vial was added five milliliters of a 5% aqueous saccharide solution, and the vials were sealed with a butyl rubber stopper, and heated for 15 min in a boiling water bath. Trehalose, maltitol, glucose, fructose, xylose, sorbitol, sucrose, maltose, and neotrehalose were used as saccharides. After cooled to ambient temperature, the vials were heated at 80xc2x0 C. for five minutes in a preheated heat-block, followed by sampling two milliliters of head-space gas in each vial with a gas syringe for analyzing volatile components on gas chromatography (GLC). The apparatuses and conditions used in the GLC analysis were: xe2x80x9cGC-14Bxe2x80x9d, a GLC apparatus commercialized by Shimadzu Techno-Research, Inc., Kyoto, Japan; xe2x80x9cCAPILLARY COLUMN TC-FFAPxe2x80x9d, a column for analysis having 0.53 mm in diameter, 30 m in length, and one micrometer thick, commercialized by GL Sciences Inc., Tokyo, Japan; a carrier gas, helium gas, at a flow rate of 10 ml/min; an injection temperature, 200xc2x0 C.; a column oven temperature, successively set to 40xc2x0 C. for five minutes and heated up to 200xc2x0 C. at an increasing temperature rate of 5xc2x0 C./min; and a hydrogen flame ionization detector as a detector. For the same samples, six veteran panels conducted the sensory evaluation.
The results are in Table 2.
As evident from the results in Table 2, it was revealed that, as compared with the system with no saccharide, trimethylamine formation was strongly inhibited in the system coexisted with trehalose and/or maltitol during boiling in water, resulting in an effective inhibition of the raw smell of chub mackerel""s meat. No trimethylamine-formation-inhibitory action was found in the system with glucose, fructose, xylose, sorbitol, sucrose, and neotrehalose. The system with maltose only showed a slight inhibitory action.
During or after boiling in water, trehalose and/or maltitol were added to chub mackerel""s meat, then the systems were compared with respect to the amount of trimethylamine present in the volatile components formed in each system. Ten grams of a mince of chub mackerel""s meat was placed in a 50-ml vial and mixed with five milliliters of a 5% solution of trehalose or maltitol corresponding to 2.5% to the mince by weight, followed by sealing the vial with a butyl rubber stopper and incubating the vial in boiling water for 15 min. In the case of incorporating both trehalose and maltitol to chub mackerel""s meat, the meat was treated similarly as above using 2.5 ml aliquots of each 5% solutions of trehalose and maltitol. The systems with such treatments were regarded as systems for coexisting saccharides during boiling in water. As a control, a system with an equal amount of water substituted for the saccharide solutions was used. Apart from these systems, 10 g of a mince of chub mackerel""s meat was placed in a 50-ml vial and admixed with five milliliters of water, followed by sealing the vial with a butyl rubber stopper, incubating the vial in boiling water for 15 min, and cooling the vial to ambient temperature. To the resulting mixture was added 0.25 g of crystal of trehalose or maltitol, d.s.b., corresponding to five milliliters of a 5% aqueous solution of each saccharide, followed by dissolving the crystal, and sealing again the vial with a butyl rubber stopper, and incubating the vial at 80xc2x0 C. for 30 min. When coexisting both trehalose and maltitol, 0.125 g, d.s.b., aliquots of each saccharide were used and treated similarly as above. The systems treated with such treatments were regarded as systems coexisted with saccharides after boiling in water. As a control, a system with no saccharide crystal was used. Head-space gases in each vial were analyzed on GLC similarly as in Experiment 2.
The results are in Table 3.
As evident from the results in Table 3, trimethylamine formation was strongly inhibited similarly as in Experiment 2 in the systems coexisted with saccharides during boiling in water as compared with the control system with no saccharide, independently of the presence of trehalose and/or maltitol. The systems coexisted with saccharides after boiling in water showed a lower trimethylamine-formation-inhibitory-effect than the control system with no saccharide. It can be estimated that trehalose and/or maltitol inhibit trimethylamine formation during heating of raw chub mackerel""s meat to lower the formation of unpleasant raw-smell inherent to fish. Considering systematically the results in Experiments 1 to 3, unlike the inclusion action on fish smell by cyclodextrins, it can be concluded that the action of inhibiting the raw-fish-smell by coexisting trehalose and/or maltitol during boiling raw-fish-meat in water positively inhibits trimethylamine formation per se from trimethylamine oxide contained in fish meat. As a timing for coexisting trehalose and/or maltitol, it is important to coexist these saccharides in edible parts of fishery products when trimethylamine is to be formed. In other words, it can be speculated that in the case of coexisting the above saccharides in a system containing trimethylamine once-formed, only expected is a partial masking effect.
A chub mackerel""s meat was minced with a mincer, and 10 g aliquots of the resulting mince were placed in 50-ml vials. To each vial were added five milliliters of five percent aqueous trehalose solutions containing 0.5, 1 and 2 g hydrous crystalline trehalose corresponding to 5%, 10% and 20% to the mice by weight, respectively, and the vials were sealed with a butyl rubber stopper, and heated for 15 min in a boiling water bath. After cooled to ambient temperature, the vials were heated at 80xc2x0 C. for five minutes in a preheated heat-block, followed by sampling the head-space gas in each vial with a gas syringe for analyzing trimethylamine and ethyl mercaptan on GLC. For trimethylamine and ethyl mercaptan analyses, one milliliter of the sampled head-space gas was analyzed on GLC similarly as in Experiment 2. While five milliliters of the sampled head-space gas was injected to xe2x80x9cGASTEC NO.72Lxe2x80x9d, a glass-detection tube for ingredient analysis, commercialized by GL Science, Tokyo, Japan, for measuring the concentration of ethyl mercaptan. As controls, there provided and tested similarly as above using a system with no saccharide and another system with 10% or 20% anhydrous crystalline sorbitol, as a comparative saccharide, with respect to the mince by weight.
The results are in Table 4.
As evident from the results in Table 4, the coexistence of trehalose inhibits the formation of trimethylamine, a specific smell of raw fishery products, and also inhibits the formation of ethyl mercaptan. It was proved that the effects by trehalose were increased positively depending on the amount of the trehalose added.